1. Field of the Invention
The present invention relates to a developing apparatus which can be used with an image forming apparatus such as an electrophotographic copying machine, an electrophotographic printer and the like.
2. Related Background Art
In image forming apparatuses of electrophotographic type, an electrostatic latent image formed on an image bearing body is visualized by a developing apparatus as a developer image.
As an example of such developing apparatuses, various dry type one-component developing apparatuses have been proposed and put to a practical use.
Nowadays, since improvement in resolution and clearness of an image have been requested, investigation regarding method and apparatus for forming a thin layer of developer (one-component developer) on a developer bearing body is inevitable and some attempts for improvement have been proposed.
For example, as disclosed in Japanese Patent Application Laid-Open No. 54-43038, an elastic blade (regulating member) made of metal or rubber abuts against a developing sleeve (developer bearing body) so that, by passing developer through an abutment area between the elastic blade and the developing sleeve to regulate the developer, a thin developer layer is formed on the developing sleeve and adequate triboelectricity is applied to the developer in the abutment area.
In this case, when non-magnetic developer is regulated by the elastic blade, a developer supplying member for supplying the developer onto the developing sleeve must be provided additionally. The reason is that, although magnetic developer can be supplied onto the developing sleeve by a force of a magnet disposed within the developing sleeve, the non-magnetic developer cannot be supplied by such a magnetic force.
To this end, a developing apparatus 50 as shown in FIGS. 7 and 8 has been proposed. In this conventional developing apparatus 50, an elastic roller 55 utilizing a foam body made of polyurethane foam or sponge or a fur brush is disposed within a developing container 54 containing non-magnetic developer 53 as a one-component developer. The roller 55 abuts against a developing roller 52 upstream of an elastic blade 51 in a rotational direction of the developing roller. By rotating the elastic roller in a direction shown by the arrow D, the developer 53 is supplied onto the developing roller 52.
As the developing roller 52 is rotated, the developer 53 supplied to the developing roller 52 is sent to an abutment area between the elastic blade 51 and the developing roller 52 to form a thin layer which is in turn used for development of an electrostatic latent image on a photosensitive body 1.
Residual developer 53 (which was not used in the development) remaining on the developing roller 52 is scraped by the elastic roller 55, and new developer is supplied to the developing roller 52 by the elastic roller 55 as mentioned above. Such operations are repeated.
In this case, when a developing roller 52 is formed from metallic material, an elastic blade 51 formed from a thin metal plate is not preferable because of wear of the developing roller. In order to provide a desired thin developer layer, rubber material such as urethane or silicone must be used.
Further, since the surface of the developing roller 52 was subjected to blasting or carbon coating treatment, good carrying of developer 53 can be achieved by moderate unevenness.
Regarding a longitudinal direction of the developing container 54, i.e., an axial direction of the developing roller 52, a roughness formed region 52a on the surface of the developing roller 52 has an area greater than an opening portion 57a of the developing container, and developing roller end seals 58 are disposed at ends of the opening portion 57a so that lateral,leakage of the developer along the longitudinal direction of the developing roller 52 is prevented while sliding the seals frictionally on the surface of the developing roller 52.
With the arrangement as mentioned above, the thin layer of non-magnetic developer can be effectively formed on the developing roller 52.
However, in comparison with a magnetic developing apparatus in which magnetic developer can easily be held on a surface of a developing roller by the action of a magnetic field, since the non-magnetic developer is used, a magnetic adsorbing force cannot be utilized. Thus, it is difficult to prevent leakage of the developer 53 out of the developing apparatus 50 shown in FIG. 8. That is to say, since the developing roller 52 cannot hold any developer other than the frictionally charged developer and an abutment area (hatched area in FIG. 8) is left between the elastic blade 51 and the developing roller 52. The developer can then easily leak outside through a lower part and ends of the developing roller 52, thereby causing developer contamination within the image forming apparatus.
To avoid this, at a developer collecting area of a lower part of the developing container 54, there is provided a flexible seal member 56 lightly abutting against the developing roller 52 and having one end secured to a frame 57 of the developing container 54, thereby permitting passage of non-used developer and preventing the developer 53 within the developing container 54 from leaking through the lower part of the container 54.
While such a developing apparatus is used with a compact copying machine or page printer, recently, in order to facilitate maintenance, a developing cartridge in which a developing apparatus is formed as a unit or a process cartridge in which a developing apparatus, a photosensitive drum, a cleaner and a charging device (not shown) are integrally incorporated has been put to practical use as an exchangeable device.
As mentioned above, the developing roller 52 has moderate unevenness obtained by surface blasting or carbon coating treatment. The developer 53 can be effectively carried by such unevenness on the surface of the developing roller 52.
However, if the developing operations using the above-mentioned conventional developing apparatus are repeated multiple times, the roughness formed region 52a on the surface of the developing roller 52 shown in FIG. 9 slides frictionally against the end peripheral seal members (leakage preventing members) 58 for preventing the developer from leaking outside. In this case, in an area corresponding to the opening portion 57a of the developing container, at both ends of a coated zone of the developing roller 52 coated by the developer, the developer is carried to the frictional sliding surfaces of the end peripheral seal members 58, with the result that the developer is melted on and adhered to the end peripheral seal members 58, thereby worsening sealing ability between the developing roller 52 and the end peripheral seal members 58. As a result, developer leakage occurs to cause serious contamination within the image forming apparatus.
An object of the present invention is to provide a developing apparatus which can prevent fusion and adhesion of developer on end leakage preventing members.
Another object of the present invention is to provide a developing apparatus in which developer born on a developer bearing body is prevented from entering into sliding surfaces of end leakage preventing members.
Yet another object of the present invention is to provide a developing apparatus which can prevent leakage of developer from end leakage preventing members.